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Adding Inkbird ITH-20R decoder to contrib directory
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Northern Man authored and Northern Man committed May 25, 2021
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/** @file
Decoder for Inkbird ITH-20R.
Copyright (C) 2018 Daniel Krueger
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
*/

/**
Decoder for Inkbird ITH-20R.
https://www.ink-bird.com/products-data-logger-ith20r.html
The compact 3-in-1 multifunction outdoor sensor transmits the data on 433.92 MHz.
The device uses FSK-PCM encoding,
The device sends a transmission every ~20 sec.
Decoding borrowed from https://groups.google.com/forum/#!topic/rtl_433/oeExmwoBI0w
Total packet length 14563 bits:
Preamble: aa aa aa ... aa aa (14400 on-off sync bits)
Sync Word (16 bits): 2DD4
Data (147 bits):
Byte Sample Comment
0-2 D3910F Always the same across devices, a device type?
3 00 00 - normal work , 40 - unlink sensor (button pressed 5s), 80 - battery replaced
4 01 Changes from 1 to 2 if external sensor present
5-6 0301 Unknown (also seen 0201), sw version?
7 58 Battery % 0-100
8-9 A221 Device id, always the same for a sensor but each sensor is different
10-11 D600 Temperature in °C * 10, little endian, so 0xD200 is 210, 21.0°C or 69.8°F
12-13 F400 Temperature °C * 10 for the external sensor, 0x1405 if not connected
14-15 D301 Relative humidity % * 10, little endian, so 0xC501 is 453 or 45.3%
16-17 38FB CRC16
18 0 Unknown 3 bits (seen 0 and 2)
CRC16 (bytes 0-15), without sync word):
poly=0x8005 init=0x2f61 refin=true refout=true xorout=0x0000 check=0x3583 residue=0x0000
To look at unknown data fields run with -vv key.
Decoder written by Dmitriy Kozyrev, 2020
*/

#include "decoder.h"

static const uint8_t preamble_pattern[] = { 0xaa, 0xaa, 0xaa, 0x2d, 0xd4 };

#define INKBIRD_ITH20R_CRC_POLY 0xA001 // reflected 0x8005
#define INKBIRD_ITH20R_CRC_INIT 0x86F4 // reflected 0x2f61


static int inkbird_ith20r_callback(r_device *decoder, bitbuffer_t *bitbuffer)
{
data_t *data;
uint8_t msg[19];

if ( (bitbuffer->num_rows != 1)
|| (bitbuffer->bits_per_row[0] < 187)
/*|| (bitbuffer->bits_per_row[0] > 14563)*/ ) {
if (decoder->verbose > 1) {
fprintf(stderr, "%s bit_per_row %u out of range\n", __func__, bitbuffer->bits_per_row[0]);
}
return DECODE_ABORT_LENGTH; // Unrecognized data
}

unsigned start_pos = bitbuffer_search(bitbuffer, 0, 0,
preamble_pattern, sizeof (preamble_pattern) * 8);

if (start_pos == bitbuffer->bits_per_row[0]) {
return DECODE_FAIL_SANITY; // Not found preamble
}

start_pos += sizeof (preamble_pattern) * 8;
unsigned len = bitbuffer->bits_per_row[0] - start_pos;

if (decoder->verbose > 1) {
fprintf(stderr, "%s start_pos=%u\n", __func__, start_pos);
fprintf(stderr, "%s len=%u\n", __func__, len);
}

if (((len + 7) / 8) < sizeof (msg)) {
if (decoder->verbose) {
fprintf(stderr, "%s %u too short\n", __func__, len);
}
return DECODE_ABORT_LENGTH; // Message too short
}
// truncate any excessive bits
len = MIN(len, sizeof (msg) * 8);

bitbuffer_extract_bytes(bitbuffer, 0, start_pos, msg, len);

// CRC check
uint16_t crc_calculated = crc16lsb(msg, 16, INKBIRD_ITH20R_CRC_POLY, INKBIRD_ITH20R_CRC_INIT);
uint16_t crc_received = msg[17] << 8 | msg[16];

if (decoder->verbose > 1) {
fprintf(stderr, "%s CRC 0x%04X = 0x%04X\n", __func__, crc_calculated, crc_received);
}

if (crc_received != crc_calculated) {
if (decoder->verbose) {
fprintf(stderr, "%s CRC check failed (0x%04X != 0x%04X)\n", __func__, crc_calculated, crc_received);
}
return DECODE_FAIL_MIC;
}

uint32_t subtype = (msg[3] << 24 | msg[2] << 16 | msg[1] << 8 | msg[0]);
int sensor_num = msg[4];
uint16_t word56 = (msg[6] << 8 | msg[5]);
int battery = msg[7];
uint16_t sensor_id = (msg[9] << 8 | msg[8]);
float temperature = (float)((int16_t)(msg[11] << 8 | msg[10])) / 10.0;
float temperature_ext = (float)((int16_t)(msg[13] << 8 | msg[12])) / 10.0;
float humidity = (float)(msg[15] << 8 | msg[14]) / 10.0;
uint8_t word18 = msg[18];

if (decoder->verbose) {
fprintf(stderr, "%s dword0-3= 0x%08X\n", __func__, subtype);
fprintf(stderr, "%s word5-6= 0x%04X\n", __func__, word56);
fprintf(stderr, "%s byte18= 0x%02X\n", __func__, word18);
}

data = data_make(
"model", "", DATA_STRING, "Inkbird ITH-20R",
"id", "", DATA_INT, sensor_id,
"battery", "Battery", DATA_INT, battery,
"sensor_num", "", DATA_INT, sensor_num,
"mic", "Integrity", DATA_STRING, "CRC",
"temperature_C", "Temperature", DATA_FORMAT, "%.1f C", DATA_DOUBLE, temperature,
"temperature2_C", "Temperature2", DATA_FORMAT, "%.1f C", DATA_DOUBLE, temperature_ext,
"humidity", "Humidity", DATA_FORMAT, "%.1f %%", DATA_DOUBLE, humidity,
NULL);

decoder_output_data(decoder, data);

return 1;
}

static char *output_fields[] = {
"model",
"id",
"battery",
"sensor_num",
"mic",
"temperature_C",
"temperature2_C",
"humidity",
NULL
};

r_device inkbird_ith20r = {
.name = "Inkbird ITH-20R temperature humidity sensor",
.modulation = FSK_PULSE_PCM,
.sync_width = 0, // No sync bit used
.short_width = 100, // Width of a '0' gap
.long_width = 100, // Width of a '1' gap
.reset_limit = 4000, // Maximum gap size before End Of Message [us]
.decode_fn = &inkbird_ith20r_callback,
.disabled = 0,
.fields = output_fields,
};

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